Forensic Science: Fundamentals & Investigations - Chapter 3 Hair Analysis

Chapter 3 Hair Analysis

Chapter Objectives

  • Identify the various parts of a hair.
  • Describe variations in the structure of the medulla, cortex, and cuticle.
  • Distinguish between human and nonhuman animal hair.
  • Determine if two examples of hair are likely to be from the same person.
  • Explain how hair can be used in a forensic investigation.
  • Calculate the medullary index for a hair.
  • Distinguish hairs from individuals belonging to broad racial categories.

Chapter 3 Vocabulary

  • Comparison microscope
  • Cortex
  • Cuticle
  • Gas chromatography
  • Hair follicle
  • Hair shaft
  • Keratin
  • Medulla
  • Melanin granules
  • Mitochondrial DNA (mtDNA)
  • Nuclear DNA

Introduction

  • A hair without the follicle and its nuclear DNA cannot provide individual evidence.
  • Hair can yield class evidence.
  • Chemical tests performed on hair can reveal drugs, toxins, heavy metals, and nutritional deficiencies.
  • mtDNA from hair can reveal some of a suspect’s or victim’s family relationships.

History of Hair Analysis

  • 1883: Alfred Swaine Taylor and Thomas Stevenson covered hair in a forensic science text.
  • 1910: Victor Balthazard and Marcelle Lambert published a comprehensive study of hair.
  • 1934: Dr. Sydney Smith analyzed hairs side by side using a comparison microscope.
  • Today: Standard procedures of hair analysis include microscopic examination and DNA analysis.

The Functions of Hair

  • Regulates body temperature
  • Decreases friction
  • Protects against sunlight
  • Acts as a sense organ
  • Humans are born with about 5 million hair follicles.

The Structure of Human Hair

  • Human hair consists of a follicle and a shaft.
  • The hair shaft is made up of three layers:
    • An inner medulla
    • A cortex
    • An outer cuticle
  • The cuticle is a transparent outer layer of the hair shaft.

Types of Hair

  • In humans, hair varies from person to person and even varies depending on its location on a particular person.
  • For an individual person, hair can vary based on its location on the body.
  • To compensate for inconsistencies that occur, 50 hairs are usually collected from a suspect’s or victim’s head.

Hair from Different Parts of the Body

  • Hair varies depending on the region of the body it originates from.

The Life Cycle of Hair

  • Hair proceeds through three stages as it develops:
    • Anagen stage
      • Lasts approximately 1000 days
    • Catagen stage
      • The hair stops growing and the follicle recedes.
    • Telogen stage
      • The hair follicle is dormant, and hair is easily lost.

Treated Hair

  • Hair can be treated in many different ways, which can alter its appearance and chemical composition.

Ethnic or Ancestral Differences

  • There are some key physical characteristics that are associated with hair of different ancestral groups.

Animal Hair and Human Hair

  • Animal hair and human hair have several differences including:
    • The pattern of pigmentation
    • The medullary index
    • The cuticle type

Hair Cuticles

  • The cuticle of the hair shaft can help distinguish human hair from other animal hair.

Electron Microscopes

  • Electron microscopes direct a beam of electrons at a sample.
  • Electron microscopes provide magnification of 50,000 times or more.

Hair Examination and Testing

  • DNA is extracted and amplified using PCR.
  • DNA is profiled using an automated process.
  • mtDNA can be used to establish a genetic relationship through the mother.
  • Suspects can be excluded if their mtDNA is not consistent with the crime-scene mtDNA.

Summary

  • Hair is a form of evidence that has been used in forensic analysis since the late 19th century.
  • Hair is a characteristic shared by all mammals and functions in temperature regulation, reducing friction, protection from light, and as a sense organ.
  • Hair consists of a follicle embedded in the skin that produces the shaft.
  • The shaft is composed of the protein keratin and consists of the outer cuticle, a cortex, and an inner medulla, most of which can vary within and among individuals and among species. The shaft also has pigments and mitochondrial DNA.
  • Hair varies in length, medulla type, and cross-sectional shape, depending on where on the body it originates.
  • Hair development is divided into three stages: anagen (growth), catagen (resting), and telogen (dormancy).